Engine control system

ABSTRACT

The present invention has an object to effectively prevent deterioration of combustion characteristics when engine temperature is low. There is provided an intake pressure controller  24  that effects control such that, when an operating condition discriminator  21  that identifies engine temperature identifies low engine temperature after engine start-up, control by an engine controller (feedback controller  23 ) that performs engine control on fluctuation of intake negative pressure to decrease the intake negative pressure is suppressed until the temperature of the intake passage rises to at or above a predetermined value, and such that the intake negative pressure is made larger.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an engine control system thatcontrols the operating condition of an engine mounted in an automobileetc.

[0003] 2. Description of the Related Art

[0004] Conventionally, as illustrated in for example Laid-open JapanesePatent Publication No. Hei 7-332132, in an engine control systemarranged so as to control the idling speed of the engine by adjustingthe rate of intake passing through the engine intake bypass passage,rise in engine speed was curbed by lowering the torque generatedimmediately after start-up by lowering the bypass intake rate for apredetermined time by a predetermined amount in response to enginetemperature, when a predetermined engine speed had been reached, afterstart-up of engine operation.

[0005] Also, the engine control system as described in the abovepublication is constructed such that, when the engine temperature dropsbelow a predetermined value, the rate of intake that is admitted to theengine combustion chamber is increased by inhibiting the aforesaidcontrol for lowering the bypass intake rate, in order to maintain anoptimum condition in regard to fuel consumption.

[0006] However, in the idling condition of the engine, basically, therate of intake is small, so when, as mentioned above, the enginetemperature is low, even if control is exercised so as to increasesomewhat the rate of intake admitted into the combustion chamber of theengine, there is the problem that no particularly large effect canregard to accelerating vaporization and atomization of the fuel by theair current can be expected; rather, since the intake air negativepressure is small, vaporization and atomization of the fuel adhering tothe intake passage are poor and combustion characteristics deteriorate.It should be noted that, when heavy gasoline of high density is employedas fuel, there is the problem that, if the intake and negative pressureis lowered by increasing the intake rate as described above, fuelcombustion characteristics are severely impaired.

SUMMARY OF THE INVENTION

[0007] In view of the above, an object of the present invention is toprovide an engine control system wherein deterioration of combustioncharacteristics when engine temperature is low can be effectivelyprevented.

[0008] In order to achieve the above object, an engine control system,according to the invention, comprises temperature discrimination meansthat identify engine temperature and intake pressure control means that,when said temperature discrimination means identifies low enginetemperature after engine start-up, executes control to increase theintake negative pressure with respect to the normal level until thetemperature of an intake passage has risen to at or above apredetermined value.

[0009] With the above construction, when the temperature discriminationmeans identifies low engine temperature after engine start-up, theintake pressure control means executes control whereby the intakenegative pressure is made larger than normally, until the temperature ofthe intake passage has risen to at or above the predeterminedtemperature, thereby promoting vaporization and atomization of fueladhering to the intake passage, so good combustion characteristics ofthe fuel can be ensured.

[0010] These and other objects, features and advantages of the presentinvention will become more apparent upon reading of the followingdetailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a diagram illustrating the overall construction of anengine provided with an engine control system according to an embodimentof the present invention;

[0012]FIG. 2 is a block diagram illustrating a specific construction ofthe engine control system;

[0013]FIG. 3 is a flow chart illustrating the first half of the controloperation that is performed by an engine control system according to thepresent invention;

[0014]FIG. 4 is a flow chart illustrating the second half of the controloperation that is performed by an engine control system according to thepresent invention;

[0015]FIGS. 5A, 5B, and 5C are time charts, each of which illustratingthe control operation that is performed by an engine control systemaccording to the present invention;

[0016]FIGS. 6A and 6B are time charts, each of which illustrating thecontrol operation that is performed by an engine control systemaccording to the present invention;

[0017]FIG. 7 is a graph illustrating the relationship between intakenegative pressure and the feedback control value; and

[0018]FIG. 8 is a flow chart illustrating a further example of thecontrol operation that is performed by an engine control systemaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019]FIG. 1 is a diagram of an engine provided with an engine controlsystem according to an embodiment of the present invention. This engineis provided with an engine body 1, intake passage 2, and exhaust passage3. On this intake passage 2, there are provided, in order from theupstream side, an air cleaner 4, air flow meter 5, throttle valve 6,surge tank 7, and fuel injector 8.

[0020] On intake passage 2, there is provided a bypass passage 9 thatbypasses the section where throttle valve 6 is arranged; an idlingcontrol valve 10 is arranged on this bypass passage 9. The rate ofintake that is admitted to combustion chamber 12 of engine body 1through bypass passage 9 is arranged to be controlled by idling controlvalve 10 being controlled in accordance with a control signal that isoutput from the engine control unit (ECU) 11.

[0021] Negative pressure sensor 27 comprising a negative pressure sensorthat detects intake negative pressure is provided in surge tank 7; onthe downstream side of surge tank 7, there is provided an intake shuttervalve 13 that opens and closes intake passage 2. This intake shuttervalve 13 is arranged so as to be driven to effect opening or closure inaccordance with a control signal from ECU 11, and is provided on thesecond passage side of intake passage 2, which is branched into a firstpassage and second passage. When the second passage is closed by thisintake shutter valve 13, the flow rate of the intake supplied intocombustion chamber 12 from the side of the first passage is increased,causing a swirl to be generated.

[0022] Also, in this engine, there is provided vaporized fuel supplymeans comprising a canister 14 that intakes vaporized fuel generated ina fuel tank, not shown, a purge passage 15 that supplies the vaporizedfuel stored in this canister 14 into a surge tank of intake passage 2,and a purge valve 16 that opens and closes this purge passage 15. Thus,the flow of vaporized gas with respect to combustion chamber 12 ofengine body 1 is controlled by driving purge valve 16 in accordance withthe control signal which is output from ECU

[0023] In addition, in the cylinder head of engine body 1, there isprovided a PCV valve 17 constituting a blow-by gas return flow device;blow-by gas that is delivered from this PCV valve 17 is thus arranged tobe supplied into surge tank 7 of intake passage 2 through blow-by gaspassage 18.

[0024] In ECU 11, as shown in FIG. 2, there are provided: operatingcondition discriminator 21 that identifies the operating condition ofthe engine; air flow rate controller 22 that controls the rate of intakein accordance with the engine operating condition; feedback controller23 that performs control such that the engine speed coincides with thetarget idling speed, by adjusting the rate of intake during engineidling operation; intake pressure controller 24 that exercises controlsuch that the intake negative pressure becomes large after enginestart-up, if required; and ignition timing controller 25 that controlsthe fuel ignition timing in accordance with operating condition of theengine.

[0025] The operating condition discriminator 21 has the function of atemperature identifier that identifies engine temperature using forexample a detection signal of a cooling water temperature sensor 20 thatdetects the cooling water temperature of the engine, and a function ofidentifying whether or not the engine is in idling operating condition,using an engine speed sensor that detects the engine speed and thedetection signal of a throttle sensor that detects the degree of openingof throttle valve 6. Also, the operating condition discriminator 21 isarranged to identify whether the fuel vaporization and atomization arein an unsatisfactory condition or not, by determining whether or not thechange of angular velocity of the output shaft is at or above apredetermined value, using the detection signal of a crank angle sensor.

[0026] Air flow rate controller 22 is arranged to control the rate ofintake supplied into combustion chamber 12 of engine body 1, byadjusting the rate of air passing through bypass passage 9, byoutputting a control signal responsive to engine operating condition tothe actuator of an idling control valve 10.

[0027] When operating condition discriminator 21 determines that theengine is in an idling operating condition, feedback controller 23 isarranged so as to perform feedback control so as to make the enginespeed coincide with the target idling engine speed by calculating afeedback control quantity of idling control valve 10 in accordance withthe deviation between the actual engine speed and the target idlingengine speed and adjusting the intake rate in accordance with thisfeedback control quantity.

[0028] Intake pressure controller 24 is arranged such that, when afterengine start-up the operating condition discriminator 21 determines thatthe engine temperature is low, it increases the rate of intake comparedwith that under normal conditions, by suppressing control in thedirection of increasing intake rate by feedback controller 23 during theperiod in which the temperature of intake passage 2 comprising an intakeport etc formed in the cylinder head or in the vicinity of the fuelinjector 8 has risen to at or above a predetermined value.

[0029] Specifically, in the aforesaid idling operating condition of theengine, if the engine speed is lower than the target idling engine speedi.e. when the engine is in an operating condition of elevated enginespeed produced by increased rate of intake, it is arranged that theidling control valve 10 is not driven in the direction of increasingrate of intake i.e. in the opening direction, by for example disablingthe feedback control of the rate of intake by the feedback controller23; in this way, it is arranged that the intake negative pressure in thecombustion chamber 12 becomes larger than normally.

[0030] Also, intake pressure controller 24 is arranged such that, if,after engine start-up, operating condition discriminator 21 determinesthat the engine temperature is low, it executes control so as topositively increase the intake negative pressure beyond the normalvalue, by driving idling control valve 10 in a closing direction, bydecreasing the demanded air flow rate set by air flow rate controller 22until the temperature of intake passage 2 has risen to at or above apredetermined value.

[0031] It should be noted that the intake pressure controller 24, if itis found that the engine temperature after engine start-up is low, ifoperating condition discriminator 21 determines that fuel vaporizationand atomization is in an unsatisfactory condition, for example only ifit is found that there is a condition of large changes of angularvelocity of the output shaft due to fuel of high density being employed,until the temperature of the intake passage 2 rises to at or above apredetermined value, suppresses the control performed by feedbackcontroller 23 to increase the rate of intake, and executes control suchas to lower the demanded air flow rate set by the air flow ratecontroller 22.

[0032] Ignition timing controller 25 is arranged so as to set an optimumignition timing in response to engine operating condition such thatnormally, fuel vaporization and atomization are not in an unsatisfactorycondition. Thus, when, during ordinary operation, the engine temperatureis found to be low after engine start-up, control is exercised such thatthe ignition timing angle of the ignition plug 19 is delayed until thetemperature of intake passage 2 has risen to at or above a predeterminedvalue. In normal operation, when timing angle delay control by ignitiontiming controller 25 is executed, control is executed by air flow ratecontroller 22 in order to increase the rate of intake so as tocompensate for the drop of engine torque corresponding to this angledelay control.

[0033] Also, if it is found that the engine temperature is low afterengine start-up, ignition timing controller 25 is arranged so as toexecute feedback control such that the engine speed coincides with thetarget idling engine speed, by advancing the ignition timing in responseto suppression of the control performed by the feedback controller 23 inthe direction in which the intake negative pressure becomes smaller,until the temperature of the intake passage 2 rises to at or above apredetermined value.

[0034] The control operation performed by the engine control system willnow be described with reference to the flow chart shown in FIG. 3 andFIG. 4. When the above control operation is commenced, after the varioussensor detection signals etc have been read (step S1), it is ascertainedwhether or not engine start-up has been completed (step S2), using thedetection signal of the starter sensor etc. If the result obtained inthis step S2 is NO, the intake air control quantity for engine start-up(ISC control quantity) is calculated (step S3) and the ignition timingfor engine start-up is calculated (step S4).

[0035] If in step S2 Yes is found, confirming that engine start-up hasbeen completed, the target engine speed n0 corresponding to the enginecondition, the intake flow rate (ISC air flow rate) and basic ignitiontiming are calculated (steps S5, S6 and S7). If for example the engineis under no-load condition, the target engine speed n0 is calculatedusing a map which is set beforehand, taking the cooling watertemperature TW of the engine as a parameter; the value of the targetengine speed n0 is set to a larger value, the lower the cooling watertemperature TW of the engine. Also, the ISC air flow rate is calculatedusing a map which is set beforehand, taking for example the targetengine speed n0 as a parameter; it is set to a larger value, the largerthe value of the target engine speed n0.

[0036] Next, the operating condition discriminator 21 identifies whetheror not (step S8) the engine cooling water temperature TW is less than apredetermined value “t”. This predetermined value “t” is the temperatureof the cooling water providing a standard for evaluation of whether ornot engine warm-up has been completed and is set for example at about40° C.

[0037] If in this step S8 YES is determined i.e. it is determined thatthe engine temperature is low, it is ascertained whether or not thecondition is that in which control after engine start-up has beencompleted, by determining (step S9) whether or not the engine speed isat or above a predetermined value n, for example 2000 rpm. If thedetermination result in this step S9 is YES, the amount of delay of theignition timing angle needed in order to accelerate engine warm-up iscalculated (step S10) and the value of the amount of increase (ISCincrease amount value) of the intake flow rate corresponding this amountof ignition timing angle delay is calculated (step S11).

[0038] After this, a determination is made (step S14) as to whether ornot the conditions for execution of feedback control (F/B) by feedbackcontroller 23 are established; if the result of the determination isYES, a determination is made as to whether or not the engine speed “ne”is less than the target idling engine speed n0 (step S1 5). If, in thisstep S15, the result of the determination is YES, a determination ismade as to whether or not the condition has been reached prior toelevation of the temperature of the intake passage 2 to at or above thepredetermined temperature i.e. at or above the temperature at which fuelvaporization and atomization can be sufficiently promoted even withoutperforming the above intake negative pressure control, by ascertaining(step S16) whether or not the time is within the predetermined periodafter engine start-up.

[0039] If in this step S16 the result of the determination is YES i.e.it is confirmed that the time is within the predetermined time afterengine start-up, a determination is made (step S17) as to whether or notthe angular speed variation Δw of the output shaft is larger than thepredetermined value “s”. If the result of the evaluation in this stepS17 is YES i.e. it is ascertained that the engine is in a condition inwhich changes of engine speed are large, due for example to use of fuelof high density, feedback of the intake flow rate by feedback controller23 is inhibited (step S18). As a result, a feedback control value in thedirection such as would increase the intake flow rate is prevented frombeing set, so control in the direction to reduce the intake negativepressure is suppressed.

[0040] Also, using the deviation between the engine speed “ne” and thetarget engine speed n0, air flow rate controller 22 calculates areduction value (ISC reduction amount value) for reducing the demandedair flow rate that has been set (step S19), and calculates the amount ofadvance of ignition timing angle (step S20) in order to effect acorresponding rise in the engine speed “ne”. Normally, when the intakerate is lowered, engine speed is lowered, but, in step S19, when it isbelieved that engine speed is in a lowered condition due todeterioration of fuel vaporization and atomization caused by the use offuel of high density and low engine temperature in the predeterminedperiod after engine start-up the rate of intake is therefore lowered,increasing the intake negative pressure and consequently promoting fuelvaporization and atomization and contrariwise making it possible tosuppress the drop of engine speed.

[0041] On the other hand, if in step S16 the result of the determinationis NO i.e. it is found that the temperature of intake passage 2 hasreached a predetermined value or more on lapse of a predetermined timeafter engine start-up, or in step S17 the result of the determination isNO, if it is ascertained that the angular speed variation Δw of theoutput shaft is of a predetermined value “s” or more, feedback controlof the intake flow rate by feedback controller 23 is commenced and theISC F/B control quantity i.e. the value of increase in the rate ofintake is calculated (step S21); processing then shifts to step S20, inwhich the lead angle amount of the ignition timing required in order toincrease the engine speed “ne” is calculated.

[0042] Also, in step S15 if the result of the determination is NO i.e.it is found that the engine speed “ne” is greater than or equal to thetarget idling speed n0, the ISC F/B control quantity for executingfeedback control by the feedback controller 23 of the intake flow ratei.e. the reduction value of the intake for lowering the engine speed“ne” is calculated (step S22) and it is then ascertained whether or notthe time is within the predetermined period after engine start-up (stepS23).

[0043] If in step S 23 the result of the determination is YES i.e. it isfound that the time is within the predetermined time after enginestart-up, a determination is made (step S24) as to whether or not theangular speed variation Δw of the output shaft is greater than thepredetermined value “s”; if the result of this determination is YES,feedback control of the ignition timing by ignition timing controller 25is inhibited (step S25). The reason for thus disabling of feedbackcontrol of the ignition timing is that, if the ignition timing werereturned, the ISC F/B control quantity i.e. the amount of reduction ofintake calculated in step S22 would be made smaller; this is thereforeprevented.

[0044] On the other hand, in step S23, if the result of thedetermination is NO i.e. if it is found that the temperature of theintake passage 2 has reached at or above the predetermined value afterthe lapse of the predetermined time after engine start-up, or if in stepS24 the result of the determination is NO i.e. it is found that theangular speed variation Δw of the output shaft is at or above thepredetermined value “s”, the amount of delay of the ignition timingangle necessary to lower the engine speed “ne” is calculated (step S26).

[0045] Thus, the final ignition timing is calculated (step S 27) basedon the basic ignition timing calculated in step S7, the amount ofignition timing delay angle calculated in step S10, and the ignitiontiming lead angle amount calculated in step S20 or ignition timing delayangle amount calculated in step S26, and the final ISC control quantityis calculated (step S28) based on the ISC air flow rate calculated instep S6, the ISC rate increase value calculated in step S11, the ISCrate decrease value calculated in step S19, and the ISC F/B controlvalue calculated in step S21 or step S22, and control signalscorresponding to these final ignition timing and final controlquantities are respectively output (step S29) to the ignition plug 19and ISC control valve 10.

[0046] As described above, after engine start-up, if the result of thedetermination in step S17 is YES i.e. the temperature identifying meansconstructed by operating condition discriminator 21 finds that theengine temperature is low, and the result of the determination in stepS8 is YES i.e. it is found that the angular speed variation Δw of theoutput shaft is larger than predetermined value “s”, until the result ofthe determination in step S16 is NO i.e. it is confirmed that thetemperature of the intake passage 2 has risen to at or above thepredetermined value, control in the direction such as to weaken theintake negative pressure performed by feedback controller 23 i.e.control such as to increase the intake flow rate is inhibited andcontrol such as to positively increase the intake negative pressure i.e.control such as to decrease the demanded amount of intake air set by theair flow rate controller 22 are executed, thereby ensuring thatsufficient intake negative pressure is maintained within the intakepassage in the vicinity of the intake port and within combustion chamber12.

[0047] On the other hand, if the result of the determination in step S8is NO i.e. it is found that the engine is in the warm-up condition, adetermination is made (step S30) to establish whether or not theconditions for execution of feedback control (F/B) by feedbackcontroller 23 are established; if the result of this determination isYES, the ordinary feedback control during engine idling operation isexecuted, by calculating the ISCF/B control quantity and the ignitiontiming F/B control value required to make the engine speed “ne” equal tothe target idling speed n0 (steps S31,S32).

[0048] Also, if the result of the determination in step S30 is NO i.e.it is found that the conditions for feedback control (F/B) are notestablished, the ISCF/B control and ignition timing F/B control areinhibited (steps S33, S34) and the ordinary intake air flow rate controland ignition timing control corresponding to the engine operatingcondition are performed.

[0049] As described above, owing to the provision of engine controllercomprising feedback controller 23 that perform engine control onfluctuation of the intake negative pressure, temperature identifyingmeans comprising operating condition discriminator 21 that identifiesthe engine temperature, and intake pressure controller 24 thatsuppresses performance of intake negative pressure control by thisfeedback controller 23, when, after engine start-up, this operatingcondition identifier 23 identifies low engine temperature, until thetemperature of the intake passage 2 rises to at or above thepredetermined value, the intake pressure controller 24 is arranged tosuppress the control performed by feedback controller 23 in thedirection such as would make the intake negative pressure smaller, sothat the intake negative pressure becomes larger than normally;consequently, the advantage is obtained that even if gasoline of highdensity is employed as fuel, deterioration of combustion characteristicscan be effectively prevented.

[0050] Specifically, if the engine temperature after start-up is lowand, as shown by the broken line in FIG. 5A, the engine speed “ne” atthe time point t1 where control after engine start-up ceases is smallerthan the target engine speed n0, conventionally, in order to raise theengine speed “ne” in response to this deviation, as shown by the brokenline in FIG. 5B, control was exercised so as to increase the intake rateISC; as a result, the intake negative pressure boost tended to becomesmall as shown by the broken line in FIG. 5C. As a result, it was notpossible to effectively promote fuel vaporization and atomization,resulting in the problems that fuel combustion characteristics becamepoor and, as shown by the broken line in FIG. 6A, fluctuations andvariations Δw of the output shaft became marked and, as shown by thebroken line in FIG. 5A, the engine speed “ne” fell.

[0051] If, to deal with this, a construction is adopted to hold theintake negative pressure boost at a large value as shown by the solidline in FIG. 5C by inhibiting the control which would increase theintake flow rate ISC as shown by the solid line in FIG. 5B until thetemperature in the intake passage to rises to at or above apredetermined value (t1 to t2), when low engine temperature isidentified after engine start-up, vaporization and atomization of fueletc adhering to the intake passage 2 because of the low pressure withincombustion chamber 12 can be promoted. As a result, the advantage isobtained that, as shown by the solid line in FIG. 6A, by maintaining thecombustion characteristics of the fuel in a good condition, angularfluctuations and variations Δw of the output shaft can be suppressedand, as shown by the solid line in FIG. 5A, lowering of the engine speed“ne” can be prevented.

[0052] In particular, in this embodiment, since a construction isadopted such that diminution of the intake negative pressure issuppressed by disabling the control exercised by the engine controllerconsisting of feedback controller 23 that directly controls the intakeair flow rate, after engine start-up it is possible for the temperatureidentification means consisting of operating condition discriminator 21,if this identifies low engine temperature, to perform control such as tomaintain the combustion characteristics in a good condition byeffectively suppressing the diminution of the intake negative pressureuntil the temperature of the intake passage 2 has risen to at or abovethe predetermined value.

[0053] Also, if a construction is adopted as illustrated in the aboveembodiment whereby if low engine temperature is identified after enginestart-up, as shown in FIG. 6B ignition timing controller 25 executesfeedback control such as to make the engine speed “ne” coincide with thetarget idling speed n0 by controlling (advancing the angle) of theignition timing until the temperature of intake passage 2 has risen toat or above a predetermined temperature, the benefit is obtained thateven though diminution of the intake negative pressure has been arrangedto be suppressed by disabling the control exerted by feedback controller23 as described above, occurrence of the situation that the engine speed“ne” greatly departs from the target engine speed n0 can be effectivelyprevented, making it possible to stabilize the engine speed “ne”.

[0054] By controlling the fuel injection amount that is injected fromfuel injector 8 by fuel injection controller, not shown, instead ofcontrol of the ignition timing or together with this control of ignitiontiming, even if an arrangement is adopted in which feedback control suchas to make the engine speed “ne” coincide with the target idling enginespeed n0 is performed, it is possible to prevent occurrence of thesituation that the engine speed “ne” greatly departs from the targetengine speed n0, thereby effectively stabilizing the engine speed “ne”.

[0055] Also, instead of the embodiment described above wherein when lowengine temperature is identified after engine start-up, in step S18,control by feedback control means 23 is inhibited until the temperatureof intake passage 2 has risen to at or above the predetermined value,thereby suppressing the diminution of intake negative pressure and instep S19 the demanded air flow rate is reduced, a construction may beadopted wherein control in the direction such as to increase the intakerate is suppressed by altering the control characteristic of thefeedback controller 23 in accordance with the detection value of thenegative pressure sensor.

[0056] For example a construction may be adopted whereby, as shown inFIG. 7, the feedback control gain that is set by the feedback controller23 is altered in response to the intake negative pressure detected bynegative pressure sensor 27 so that, when this intake negative pressureis small, control in the direction such as to increase the intake airflow rate is suppressed by setting the gradient of the graph that isused to set the control gain a, i.e. the feedback control quantity inthe increasing region of intake flow rate in which the speed deviationbetween the target engine speed and the actual engine speed is negative,to a smaller value than the control gain b when the intake negativepressure is large.

[0057] Also, as shown in FIG. 7, if the intake negative pressuredetected by negative pressure sensor 27 is small, it is possible tosuppress control in the direction such as to increase the intake airflow rate, by setting the upper limiting value al of the feedbackcontrol quantity in the region of increasing intake amount in which thespeed deviation between the target engine speed and actual engine speedis negative to a value smaller than the upper limiting value b1 when theintake negative pressure is large.

[0058] If it is found as above that the intake negative pressure issmall and the engine temperature after engine start-up is low, it ispossible to effectively promote vaporization and atomization of fueladhering to the intake passage by setting the feedback control gain ofthe intake air flow rate used by the feedback controller 23 to a smallvalue until the temperature of the intake passage 2 has risen to at orabove a predetermined value; increase in the intake flow rate can alsobe suppressed in a straightforward and effective manner by adopting aconstruction in which the upper limiting value thereof is set to a smallvalue.

[0059] Also, with the above embodiment, a construction is adoptedwhereby, if it is found that the engine temperature is low after enginestart-up, control is exercised by intake pressure controller 24 so as tosuppress control by the engine controller comprising feedback controller23 in the direction such as to decrease the intake negative pressure,until the temperature of intake passage 2 has risen to at or above orthe predetermined value, and the demanded air flow rate set by air flowrate controller 22 is reduced, thereby positively reducing the intakeair flow rate; consequently, the advantage is obtained that intakenegative pressure is effectively increased and the vaporization of thefuel can therefore be promoted.

[0060] It should be noted that, instead of the above embodiment, whichwas constructed such that intake negative pressure could be increased byadjusting the intake air flow rate by controlling the feedbackcontroller 23 or air flow rate controller 22 by the intake pressurecontroller 24, it would be possible to adopt a construction in whichintake negative pressure is increased by driving an intake flow controlvalve comprising intake shutter valve 13 that controls intake flow inthe second passage of intake passage 2 in a closing direction, or bydriving a flow control valve comprising purge valve 16 that controls theflow of auxiliary fluid comprising vaporized fuel that is admitted intocombustion chamber 12 in a closing direction.

[0061] For example, as shown in the flow chart of FIG. 8, after readingthe detection signals etc of the various sensors (step S41), operatingcondition discriminator 21 identifies whether or not the cooling watertemperature TW of the engine is less than a predetermined value “t”(step S42) and, if the result of this determination is YES, adetermination is performed (step S43) as to whether or not apredetermined time has elapsed after engine start-up. The same benefitsas in the above embodiment can also be obtained with a construction inwhich, when the result of the determination in step S43 is YES,admission of vaporized fuel into combustion chamber 12 is restricted byputting purge valve 16 into closed condition and intake flow isrestricted by putting intake shutter valve 13 into closed condition,thereby positively increasing the intake negative pressure until thetemperature of intake passage to rises to at or above the predeterminedvalue, if after engine start-up the operating condition discriminator 21determines that engine temperature is low.

[0062] It should be noted that the same benefits as in the aboveembodiment can be obtained by adopting a construction wherein a flowcontrol valve comprising an opening/closing valve 26 is provided in ablow-by gas passage 18 as shown by the broken line in FIG. 1 and, ifoperating condition discriminator 21 determines that the enginetemperature is low after engine start-up, it is arranged to positivelyintensify the intake negative pressure by restricting the inflow ofblow-by gas into the combustion chamber 12, by driving the flow controlvalve comprising opening/closing valve 26 in a closing direction untilthe temperature of intake passage 2 has reached at or above thepredetermined value.

[0063] Also, in the above embodiment, in which it is arranged for intakecontroller 24 to perform control such as to increase the intake negativepressure if low engine temperature is identified after engine start-up,until the temperature of intake passage 2 has reached at or above apredetermined value, it is desirable to adopt a construction such as toexecute feedback control so as to make the engine speed “ne” coincidewith the target idling speed n0 by using ignition timing controller 25to control the ignition timing or by using a fuel injection controller,not shown, to control the fuel injection rate, in order to make itpossible to stabilize the engine speed “ne” by preventing occurrence ofthe situation that there is a large discrepancy between engine speed“ne” and the target speed n0.

[0064] Furthermore, in the above embodiment, owing to the adoption of aconstruction such that elevation of the temperature of the intakepassage 2 to at or above a predetermined value is detected based onlapsed time after engine start-up, there is the advantage that theperiod of disabling of control such as to suppress diminution of theintake negative pressure by the intake pressure controller 24 or ofcontrol such as to make the intake negative pressure large can beappropriately determined by a straightforward construction. It should benoted that, instead of the above embodiment, it could be arranged todetect whether or not the temperature of intake passage 2 has risen toat or above the predetermined temperature by using the detected value ofa temperature sensor that detects the engine cooling water temperatureTW or exhaust gas temperature.

[0065] Also, the adoption of a construction as in the embodimentdescribed above such that intake pressure controller 24 suppressescontrol which would decrease the intake negative pressure with respectto the normal level and executes control which positively increases theintake negative pressure until the temperature of the intake passage 2has risen to at or above a predetermined value only when operatingcondition discriminator 21 has ascertained that the engine temperatureafter engine start-up is low and, based on angular speed variation Δw ofthe output shaft, that vaporization and atomization of the fuel are inan unsatisfactory condition has the advantage that, in a condition inwhich fuel vaporization and atomization are good, execution of controlby the intake pressure controller 24 can be prevented from interferingwith idling speed control and, in a condition in which fuel vaporizationand atomization are poor, good combustion characteristics can be ensuredby appropriate execution of control by intake pressure controller 24.

[0066] It should be noted that, in place of the above embodiment whichis arranged so that whether or not fuel vaporization and atomization arein a poor condition is ascertained based on the angular speed variationΔw of the output shaft, an arrangement could be adopted wherein whetheror not fuel vaporization and atomization are in a poor condition isascertained based on a lowered condition of engine speed, a leancondition of the air/fuel ratio, or high fuel density.

[0067] Also, with the above embodiments, since these are constructedsuch that, on identification of low engine temperature after enginestart-up in a condition with good fuel vaporization and atomization,control is arranged to be performed by the aforesaid ignition timingcontroller 25 to raise the exhaust gas temperature by delaying theignition timing angle, and that control is arranged to be performed byair flow rate controller 24 to raise the engine output by increasingintake air flow rate in correspondence with this ignition timing angledelay control, there is the advantage that early activation of theexhaust gas cleaning catalyst which is arranged in exhaust passage 3 canbe achieved without lowering engine output.

[0068] Also, as described above, if low engine temperature after enginestart-up is identified in a condition with poor fuel vaporization andatomization, since the intake negative pressure is weakened in responseto increase in this intake air flow rate when control such as toincrease the intake air flow rate in response to this ignition timingangle delay control is performed by air flow rate controller 24 untilthe temperature of the intake passage 2 has risen to at or above apredetermined value, the advantage is obtained that a marked benefiti.e. a marked benefit in terms of promoting fuel vaporization andatomization is achieved by suppressing control to diminish intakenegative pressure by intake pressure controller 24 or by executingcontrol to increase intake negative pressure.

[0069] Summing up the aforementioned disclosures, one aspect of thepresent invention comprises temperature discrimination means thatidentify engine temperature and intake pressure control means that, whensaid temperature discrimination means identifies low engine temperatureafter engine start-up, executes control to increase the intake negativepressure with respect to the normal level until the temperature of anintake passage has risen to at or above a predetermined value.

[0070] With the above construction, when the temperature discriminationmeans identifies low engine temperature after engine start-up, theintake pressure control means executes control whereby the intakenegative pressure is made larger than normally, until the temperature ofthe intake passage has risen to at or above the predeterminedtemperature, thereby promoting vaporization and atomization of fueladhering to the intake passage, so good combustion characteristics ofthe fuel can be ensured.

[0071] In an engine control system according to the above aspect,further comprises engine control means that executes engine control onfluctuation of intake negative pressure wherein said intake pressurecontrol means is constructed so as to increase the intake negativepressure with respect to the normal level, when, after engine start-up,said temperature discrimination means identifies low engine temperature,by suppressing control by said engine control means in the directionsuch as to diminish intake negative pressure, until the temperature ofthe intake passage has risen to at or above a predetermined value.

[0072] With the above construction, when low engine temperature afterengine start-up is identified, a sufficiently large value of the intakenegative pressure is maintained by suppressing control by the enginecontrol means in the direction such as to reduce intake negativepressure until the temperature of the intake passage has risen to at orabove the predetermined value, thereby promoting vaporization andatomization of fuel adhering to the intake passage, so good combustioncharacteristics of the fuel can be ensured.

[0073] In the aforementioned invention, the engine control means mayfurther comprise feedback control means that perform feedback control ofthe intake air flow rate such that during idling operation of the enginethe engine speed is made to coincide with the target idling engine speedand the intake pressure control means is arranged to increase intakenegative pressure with respect to the normal level by suppressingcontrol by the feedback control means in the direction such as toincrease intake air flow rate if low engine temperature after enginestart-up is identified, until the temperature of the intake passage hasrisen to at or above the predetermined value.

[0074] With the above construction, by suppressing the control by thefeedback control means in the direction such as to increase intake airflow rate when low engine temperature is identified after enginestart-up until the temperature of the intake passage has risen to at orabove the predetermined value, control to maintain the intake negativepressure at a large value can be effectively performed.

[0075] In the aforementioned invention, an engine control system mayfurther comprise negative pressure detection means that detect intakenegative pressure wherein the intake pressure control means isconstructed to suppress control in the direction such as to increase theintake air flow rate, by altering the control characteristic of thefeedback control means in accordance with the value detected by thenegative pressure detection means, when low engine temperature isidentified after engine start-up, until the temperature of the intakepassage has risen to at or above the predetermined value.

[0076] With the above construction, when low engine temperature afterengine start-up is identified, by altering the control characteristic ofthe feedback control means in accordance with the detected value of thenegative pressure detection means until the temperature of the intakepassage has risen to at or above the predetermined value, increasingcontrol of the intake air flow rate is suppressed so the intake negativepressure is maintained at a suitable value.

[0077] In the aforementioned invention, when the intake negativepressure detected by the negative pressure detection means is small, theintake pressure control means may be constructed to suppress control inthe direction such as would increase the intake air flow rate, bysetting the feedback control gain of the feedback control means in theregion of increasing intake air flow rate to a value smaller than thatwhen the intake negative pressure is large.

[0078] With the above construction, by setting the feedback control gainof the feedback control means in the region of increasing intake airflow rate to a small value when the intake negative pressure is smalland low engine temperature after engine start-up is identified, untilthe temperature of the intake passage rises to at or above thepredetermined value, increase of the intake air flow rate isappropriately and effectively suppressed, enabling vaporization andatomization of fuel etc adhering to the intake passage to be promoted.

[0079] In the aforementioned invention, when the intake negativepressure detected by the negative pressure detection means is small, theintake pressure control means may be constructed to suppress control inthe direction such as would increase the intake air flow rate, bysetting the upper limiting value of the feedback control quantity of thefeedback control means in the region of increasing intake air flow rateto a value smaller than that when the intake negative pressure is large.

[0080] With the above construction, when the intake negative pressure issmall and low engine temperature is identified after engine start-up, bysetting the upper limiting value of the feedback control quantity of thefeedback control means to a small value in the increasing region of theintake air flow rate until the temperature of the intake passage risesto at or above a predetermined value, vaporization and atomization offuel etc adhering to the intake passage is promoted by suppressingincrease of intake air flow rate in a straightforward and effectivemanner.

[0081] In the aforementioned invention, if low engine temperature isidentified after engine start-up, feedback control may be executed bycontrolling at least one of the ignition timing or fuel injection rateso as to make the engine speed coincide with the target idling enginespeed, until the intake passage temperature has risen to at or above thepredetermined value.

[0082] With the above construction, when low engine temperature isidentified after engine start-up, fuel vaporization and atomization arepromoted by the intake pressure control means executing control such asto increase the intake negative pressure with respect to the normallevel, until the temperature of the intake passage rises to at or abovethe predetermined temperature, and, by controlling at least one of theignition timing or fuel injection rate, it is possible to make theengine speed coincide with the target idling speed.

[0083] In the aforementioned invention, the engine control system mayfurther comprise air flow rate control means for controlling the intakeair flow rate in accordance with engine operating condition the intakepressure control means is constructed so as to increase the intakenegative pressure, when, after engine start-up, low engine temperatureis identified, by reducing the demanded air flow rate that is set by theair flow rate control means, until the temperature of the intake passagehas risen to at or above a predetermined value.

[0084] With the above construction, when low engine temperature isidentified after engine start-up, the intake pressure control meansexecutes control such as to positively increase the intake negativepressure by decreasing the demanded air flow rate set by the air flowrate control means until the temperature of the intake passage has risento at or above the predetermined value, so fuel vaporization andatomization are effectively promoted, and good fuel combustioncharacteristics are ensured.

[0085] In the aforementioned invention, the intake pressure controlmeans may be constructed so as to increase the intake negative pressureby driving an intake flow control valve that controls intake flow in aclosing direction when low engine temperature after engine start-up isidentified, until the temperature of the intake passage rises to at orabove the predetermined value.

[0086] With the above construction, when low engine temperature afterengine start-up is identified, the intake pressure control meansexecutes control such as to positively increase the intake negativepressure by driving the intake flow control valve in a closing directionuntil the temperature of the intake passage rises to at or above thepredetermined value, so fuel vaporization and atomization areeffectively promoted and good fuel combustion characteristics areensured.

[0087] In the aforementioned invention, the intake pressure controlmeans may be constructed so as to increase the intake negative pressureby driving a flow control valve that controls flow of auxiliary fluidcomprising vaporized fuel or blow-by gas etc that is fed into thecombustion chamber in a closing direction when low engine temperatureafter engine start-up is identified, until the temperature of the intakepassage rises to at or above the predetermined value.

[0088] With the above construction, when low engine temperature afterengine start-up is identified, the intake pressure control meansexecutes control such as to positively increase the intake negativepressure by decreasing the auxiliary fluid that is fed into thecombustion chamber, until the temperature of the intake passage rises toat or above the predetermined value, so fuel vaporization andatomization are effectively promoted and good combustion characteristicsare ensured.

[0089] In the aforementioned invention, the temperature discriminationmeans may be constructed to detect elevation of the temperature of theintake passage to at or above the predetermined value, based on thelapse of time after engine start-up.

[0090] With the above construction, whether or not the temperature ofthe intake passage has risen to at or above the predetermined value isappropriately detected by a straightforward construction, based on thelapse of time after engine start-up.

[0091] In the aforementioned invention, the engine control system mayfurther comprise operating condition discrimination means thatidentifies whether or not fuel vaporization and atomization are in anunsatisfactory condition, based on a lowered condition of engine speedor angular speed variation of the output shaft etc, and is constructedso as to execute control such as to increase the intake negativepressure only when low engine temperature after engine start-up isidentified and an unsatisfactory condition of fuel vaporization andatomization are ascertained by the operating condition discriminationmeans, until the temperature of the intake passage rises to at or abovethe predetermined value.

[0092] With the above construction, in a condition in which fuelvaporization and atomization are good, execution of control by theintake pressure control means is prevented from interfering withexecution etc of idling speed control and, if the fuel vaporization andatomization condition is unsatisfactory, the intake pressure controlmeans executes control such as to increase the intake negative pressure,thereby ensuring good combustion characteristics.

[0093] In the aforementioned invention, the engine control systemfurther comprise ignition timing control means that delays the ignitiontiming angle when low engine temperature is identified after enginestart-up and air flow rate control means that increases the intake airflow rate in response to this ignition timing angle delay control,constructed such that control of ignition timing and intake air flowrate by the timing angle control means and air flow rate control meansis executed if the operating condition discrimination means ascertainsthat fuel vaporization and atomization are not in an unsatisfactorycondition.

[0094] With this construction, if the fuel vaporization and atomizationare not in an unsatisfactory condition and low engine temperature afterengine start-up is identified, the ignition timing control meansexecutes control to delay the ignition timing angle and the air flowrate control means executes control such as to increase the intake airflow rate corresponding to this ignition timing angle delay control, soit becomes possible to activate the exhaust gas cleaning catalystprovided in the exhaust passage at an early stage without provoking adrop in engine output.

[0095] This application is based on Japanese application serial Nos.2000-298960 and 2001-78350, filed in Japanese Patent Office on Sep. 29,2000 and Mar. 19, 2001 respectively, the contents of which are herebyincorporated by reference.

[0096] Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention hereinafterdefined, they should be construed as being included therein.

What is claimed is:
 1. An engine control system comprising: temperaturediscrimination means for identifying engine temperature, and intakepressure control means, when said temperature discrimination meansidentifies low engine temperature after engine start-up, for executingcontrol to increase the intake negative pressure with respect to anormal level until the temperature of an intake passage has risen to ator above a predetermined value.
 2. The engine control system accordingto claim 1, further comprising engine control means for executing enginecontrol on fluctuation of intake negative pressure, wherein said intakepressure control means is constructed so as to increase the intakenegative pressure with respect to the normal level, when, after enginestart-up, said temperature discrimination means identifies low enginetemperature, by suppressing control by said engine control means in adirection to diminish intake negative pressure, until the temperature ofthe intake passage has risen to at or above a predetermined value. 3.The engine control system according to claim 1, wherein the enginecontrol means includes feedback control means that perform feedbackcontrol of the intake air flow rate such that during idling operation ofthe engine the engine speed is made to coincide with a target idlingengine speed, and said intake pressure control means is arranged toincrease intake negative pressure with respect to the normal level bysuppressing control by said feedback control means in a direction toincrease intake air flow rate if low engine temperature after enginestart-up is identified, until the temperature of the intake passage hasrisen to at or above the predetermined value.
 4. The engine controlsystem according to claim 3, further comprising negative pressuredetection means for detecting intake negative pressure, wherein saidintake pressure control means is constructed to suppress control in adirection to increase the intake air flow rate, by altering the controlcharacteristic of said feedback control means in accordance with thevalue detected by said negative pressure detection means, when lowengine temperature is identified after engine start-up, until thetemperature of the intake passage has risen to at or above thepredetermined value.
 5. The engine control system according to claim 4,wherein, when the intake negative pressure detected by the negativepressure detection means is small, said intake pressure control means isconstructed to suppress control in a direction to increase the intakeair flow rate, by setting the feedback control gain of said feedbackcontrol means in a region of increasing intake air flow rate, to a valuesmaller than that when the intake negative pressure is large.
 6. Theengine control system according to claim 4, wherein, when the intakenegative pressure detected by the negative pressure detection means issmall, said intake pressure control means is constructed to suppresscontrol in a direction to increase the intake air flow rate, by settingthe upper limit value of the feedback control quantity of said feedbackcontrol means in a region of increasing intake air flow rate, to a valuesmaller than that when the intake negative pressure is large.
 7. Theengine control system according to claim 4, wherein, if low enginetemperature is identified after engine start-up, feedback control isexecuted by controlling at least one of the ignition timing or fuelinjection rate so as to make the engine speed coincide with the targetidling engine speed, until the intake passage temperature has risen toat or above the predetermined value.
 8. The engine control systemaccording to claim 1, further comprising air flow rate control means forcontrolling the intake air flow rate in accordance with engine operatingcondition, wherein said intake pressure control means is constructed soas to increase the intake negative pressure, when, after enginestart-up, low engine temperature is identified, by reducing a demandedair flow rate that is set by said air flow rate control means, until thetemperature of the intake passage has risen to at or above apredetermined value.
 9. The engine control system according to claim 1,wherein said intake pressure control means is constructed so as toincrease the intake negative pressure by driving an intake flow controlvalve that controls intake flow in a closing direction when low enginetemperature, after engine start-up, is identified, until the temperatureof the intake passage rises to at or above the predetermined value. 10.The engine control system according to claim 1, wherein said intakepressure control means is constructed so as to increase the intakenegative pressure by driving a flow control valve that controls flow ofauxiliary fluid comprising vaporized fuel or blow-by gas that is fedinto the combustion chamber in a closing direction when low enginetemperature, after engine start-up, is identified, until the temperatureof the intake passage rises to at or above the predetermined value. 11.The engine control system according to claim 1, wherein said temperaturediscrimination means is constructed to detect elevation of thetemperature of the intake passage to at or above the predeterminedvalue, based on the lapse of time after engine start-up.
 12. The enginecontrol system according to claim 1, further comprising operatingcondition discrimination means that identifies whether or not fuelvaporization and atomization are in an unsatisfactory condition, basedon a lowered condition of engine speed or angular speed variation of theoutput shaft, and is constructed so as to execute control to increasesaid intake negative pressure only when low engine temperature, afterengine start-up, is identified and an unsatisfactory condition of fuelvaporization and atomization are found by said operating conditiondiscrimination means, until the temperature of the intake passage risesto at or above the predetermined value.
 13. The engine control systemaccording to claim 1, further comprising ignition timing control meansthat delays the ignition timing angle when low engine temperature isidentified after engine start-up, and air flow rate control means thatincreases the intake air flow rate in response to this ignition timingangle delay control, wherein control of ignition timing and intake airflow rate by said timing angle control means and air flow rate controlmeans is executed if said operating condition discrimination meansdetects that fuel vaporization and atomization are not in anunsatisfactory condition.
 14. An engine control system comprising:temperature discrimination unit for identifying engine temperature, andintake pressure controller, when said temperature discrimination unitidentifies low engine temperature after engine start-up, for executingcontrol to increase the intake negative pressure with respect to anormal level until the temperature of an intake passage has risen to ator above a predetermined value.
 15. The engine control system accordingto claim 14, further comprising engine controller for executing enginecontrol on fluctuation of intake negative pressure, wherein said intakepressure controller is constructed so as to increase the intake negativepressure with respect to the normal level, when, after engine start-up,said temperature discrimination unit identifies low engine temperature,by suppressing control by said engine controller in the direction todiminish intake negative pressure, until the temperature of the intakepassage has risen to at or above a predetermined value.
 16. The enginecontrol system according to claim 14, wherein the engine controllerincludes feedback controller that perform feedback control of the intakeair flow rate such that during idling operation of the engine the enginespeed is made to coincide with a target idling engine speed, and saidintake pressure controller is arranged to increase intake negativepressure with respect to the normal level by suppressing control by saidfeedback controller in a direction to increase intake air flow rate iflow engine temperature after engine start-up is identified, until thetemperature of the intake passage has risen to at or above thepredetermined value.
 17. The engine control system according to claim14, further comprising air flow rate controller for controlling theintake air flow rate in accordance with engine operating condition,wherein said intake pressure controller is constructed so as to increasethe intake negative pressure, when, after engine start-up, low enginetemperature is identified, by reducing a demanded air flow rate that isset by said air flow rate controller, until the temperature of theintake passage has risen to at or above a predetermined value.